Positive acting electron beam resist media and the use thereof in forming patterned layers in and on a variety of substrates are well known in the art. Poly(olefin sulfone) polymers are a major class of such positive electron beam resists. For example, poly(1-methyl-1-cyclopentene sulfone) has been utilized for audio/video recording apparatus as described in Poliniak et al., U.S. Pat. Nos. 3,935,331 and 3,935,332.
Poly(olefin sulfone) terpolymers and their use as electron beam resists are likewise known in the art. For example, Gipstein et al. in U.S. Pat. No. 3,898,350 disclose terpolymers formed from (a) an alpha olefin; (b) sulfur dioxide and (c) a compound selected from the group consisting of cyclopentene, bicycloheptene and methyl methacrylate.
Heretofore, the vast majority of positive electron beam resists are developed with an organic developer. The few aqueous developable positive electron beam resists known to the art are not polymeric in nature. Such resists comprise a water-soluble alkali resin and an electron beam sensitive compound as described, for example, in Ross et al., U.S. Pat. No. 4,065,306.
Without exception, poly(olefin sulfone) copolymer and terpolymer positive electron beam resists are recognized in the art as being developable with an organic developer. It will be readily appreciated that the use of an organic developer is disadvantageous in terms of cost of materials as well as potential impact on the environment. Organic developers are further disadvantageous in that their action on the resist is, in essence, a physical one, i.e., the developer penetrates interstices in the exposed portion of the polymer and causes the resist to swell. As a result of this physical development, all organic solvent developers will cause cracking in the resist to some degree, particularly with thicker films. By contrast, an aqueous developer works by chemical reaction with the exposed portions of the resist, i.e., by forming soluble salts. Therefore, cracking is not usually a problem with aqueous developers.
Another problem inherent with all positive resists, regardless of the type of developer utilized, is development latitude. Since conditions such as development time, temperature, and humidity vary to a small degree, even in the most stringently controlled environments, the development of the resist should not be ultra-sensitive to small variations in environment if high yields are to be maintained and losses minimized. Again, as a general rule for all positive resists, increased sensitivity is realized at the expense of loss of developmental latitude and vice versa.
The aqueous developable electron beam resists of this invention are highly advantageous, particularly with reference to forming patterns in materials such as chromium, in that they possess a substantially improved development latitude without loss of sensitivity and utilize a developer which is both inexpensive and non-offensive to the environment. In addition, resists formed from the poly(olefin sulfone) terpolymers of this invention adhere well to the substrate, yield highly resolved patterns after development with little erosion, and are free from cracking and swelling even in films over one micrometer in thickness.
The present invention is predicated on the discovery that inclusion of a particular cyclic organic acid in a poly(olefin sulfone) terpolymer produces a material suitable for the preparation of positive electron beam resist media which are developable with an aqueous developer. Media utilizing the terpolymers of this invention have a significantly high degree of resolution without appreciable loss of any of the desirable characteristics normally associated with poly(olefin sulfone) electron beam resists such as, for example, adhesion to the substrate. An article by Hailer et al. in J. Electrochem. Soc., January, 1979, p. 154-161, documents the art's awareness that incorporation of carboxylic acid groups into a resist material will improve adhesion of the resist to silicon, silicon dioxide and various metals utilizing a comparison between a polymethylmethacrylate/methacrylic acid polymer and a similar copolymer containing no methacrylic acid. Further, it has long been recognized in the printing industry that small amounts of carboxylic acid groups in binders improve adhesion of conventional photopolymers to aluminum and copper plates.
It is considered unexpected in the light of the above discussed teachings, that the novel terpolymers of this invention would possess the advantages conventionally associated with poly(olefin sulfone) electron beam resists and, in addition, be characterized by a significantly high degree of resolution and by being developable with an aqueous developer.